Atomic Layer Fluorination of 5 V Class Positive Electrode Material LiCoPO4 for Enhanced Electrochemical Performance

The surface fluorination of lithium cobalt phosphate (LiCoPO4, LCP) using a one-step, room temperature processable, easily up-scalable and dry surface modification method with XeF(2)as fluorine source was developed. After fluorination, fluorine-rich nanoparticles were observed mainly on the particle surface, which facilitates the improvement of surface stability and electrochemical performance such as cycling stability and rate capability, as the fluorinated LCP can be protected against side reactions with electrolyte or by-products of electrolyte decomposition at high voltage (5 V). More importantly, the direct surface fluorination proved more efficient than adding a fluorinated electrolyte additive (i. e., FEC). These results suggest that surface fluorination using XeF(2)is of great promise for practical applications of high voltage positive materials for lithium-ion batteries.